1. Field of the Invention
The present invention relates to a pressure gauge, and more particularly, pertains to a pressure gauge substantially filled with silicone gel, gelatinous material, or any other suitable materials for medical and other applications.
2. Description of the Prior Art
Hollow bourdon tube pressure gauges inherently have several problems in medical applications. First, due to the shape of the bourdon tube, it is very difficult to purge the air from the tube and replace it with a liquid. Air in the tube makes the system compliant so that added work must be done to compress the trapped air. Also, the trapped air being compressible stores energy, so if system failure occurs, this energy is suddenly released in an uncontrolled manner. In the present invention, a gel substance completely displaces the air in the tube so that no purging of the gauge is required.
Second, the standard manufacturing method for fabricating these pressure gauges is to seal the bourdon tube and also join the tube to the gauge base by soldering or brazing. Solder, an alloy of lead and tin, also contains trace amounts of other heavy metals such as antimony and/or cadmium. In medical applications, these heavy metals are known toxins which can significantly affect physiological function.
These types of gauges are used in numerous medical applications ranging from relatively remote to intimate contact with patients and/or patient fluid. For instance, these gauges are used to monitor the internal pressures of the balloon used to dilate blood vessels as in an angioplasty procedure. The only barrier between direct fluid contact between the gauge and patient is the balloon itself. If the balloon or catheter were to rupture and/or leak when the system is pressurized, and there is any air in the gauge tube, then there is an energy source to drive contaminates out of the gauge and into the patient. Even in the absence of air in the gauge tube, diffusion can move contaminates into the patient. In the present invention, the gel substance traps the contaminate in the gauge tube and prevents their migration to the patient.
Third, even in remote sensing applications, the gel filled gauge tube has a greatly reduced surface area exposed to the working fluid which eliminates the dead space or volume of the gauge tube which can harbor microbial growth. Oil filled bourdon tube gauges with an isolating diaphragm are used in many applications where the same issues as described above need to be addressed. However, these isolating diaphragms need to have a large surface area to counteract the diaphragm's inherent stiffness which ca compromise the sensitivity and accuracy of the gauge. In the present invention, the gel substance gives isolation without the need for a large surface area isolating diaphragm. This is advantageous in a system where size is critical.
In many medical applications, the system's working fluid is a saline solution with is highly corrosive to most metals. Also, the saline solution could induce electrolysis inside the bourdon tube due to the dissimilar metals used in its fabrication. This electrolysis can put heavy metal ions into solution with the saline working fluid. In the present invention, the gel substance prevents the saline solution from contracting the inside of the bourdon tube.
A current process of providing a gauge suitable for medical applications is to flush the interior of the tube with organic solvents and then install a porous filter into the entrance port of the gauge tube. This process reduces but does not eliminate the contaminates in the gauge tube. A porous filter in the prior art pressure gauges makes it more difficult to purge the air from the tube.
The present invention overcomes the disadvantages of the prior art by providing a pressure gauge including a bourdon tube substantially filled with a silicone gel, gelatinous material, or any other suitable materials for medical or other applications.